The present invention relates to an antenna device comprising capacitively coupled radiating elements and a hand-held mobile communication device comprising such an antenna in general, and more specifically to an antenna device and a hand-held mobile communication device comprising such an antenna for receiving and transmitting circularly polarized RF signals for communication with satellites.
One of the driving forces of the mobile communication industry today is availability and another is size. A user of a hand-held mobile communication device requires to be reached wherever his location may be. This puts requirements on the operator to have good coverage of their mobile network, but for large unpopulated areas this is not possible with any reasonable economy. One solution for a user who frequently travels to unpopulated locations is to instead use a satellite telephone.
Such a user will still have requirements on the size of his satellite communication device as he undoubtedly will compare his ordinary cellular communication device with his satellite communication device. Since the distance to orbiting satellites is so great the antennas used will be larger compared to antennas for cellular communication devices, and will consequently take a considerable amount of the space of a satellite communication device. The need for reducing the size of the antennas for satellite communication devices is thus large and anyone being able to reduce the size for such an antenna will have a considerable competitive advantage.
In U.S. Pat. No. 5,191,352 is a quadrifilar radio frequency antenna disclosed for receiving signals from an earth orbiting satellite. The antenna has four helical wire elements shaped and arranged so as to define a cylindrical envelope. The elements are co-extensive in the axial direction of the envelope.
WO 96/06468 discloses an antenna device with a ceramic core with a relative dielectric constant of at least 5 where every second helical element is longer so that a self-phased antenna is achieved. Every second element is made longer through a meandering shape.
In the journal Microwave Engineering Europe June/July 1995 an antenna for personal hand-held terminals is disclosed. The antenna is of quadrifilar helix type.
The following patent applications are related to the same technical field as the invention of this application, and are hereby incorporated herein by reference:
the Swedish patent application SE 9801754-4 having the title xe2x80x9cAn antenna system and a radio communication device including an antenna systemxe2x80x9d, filed in Sweden the same day as this application, May 18, 1998, applicant Allgon AB,
the Swedish patent application SE 9801753-6 having the title xe2x80x9cAntenna device comprising feeding means and a hand held radio communication device for such antenna devicexe2x80x9d, filed in Sweden the same day as this application, May 18, 1998, applicant Allgon AB, and
the Swedish patent application SE 9704938-1, filed Dec. 30, 1997, applicant Allgon AB, having the title xe2x80x9cAntenna system for circularly polarised radio waves including antenna means and interface network.xe2x80x9d
The main object of the present invention is thus to achieve an antenna for both receiving and transmitting circularly polarized RF signals, which is smaller and lighter than prior art antennas.
Another object of the present invention is to achieve one antenna for both receiving and transmitting circularly polarized RF signals which has better characteristics for a given physical length than prior art antennas.
Another object according to one embodiment of the present invention is to achieve an antenna, which can receive and transmit RF signals in two different frequency bands.
Another object according to one embodiment of the invention is to achieve one antenna for both receiving and transmitting circularly polarized RF signals within a communication system where the RF band for receiving signals and the RF band for transmitting signals is spaced apart.
The problems described above, with how to achieve a smaller and more efficient antenna for receiving and transmitting circularly polarized RF signals is solved by providing an N-helical-filar antenna with N radiating elements, where N is an integer greater than one, coaxially arranged and defining a cylindrical envelope where each individual radiating element is capacitively coupled to another radiating element.
The problems described above, with how to achieve a smaller and more efficient antenna for receiving and transmitting circularly polarized RF signals, according to one embodiment of the invention, is solved by providing an N-helical-filar antenna with N radiating elements coaxially arranged and defining a cylindrical envelope where each individual radiating element has a meandering shape superimposed on the main helical form.
In more detail the objects of the present invention, with how to achieve a smaller and more efficient antenna for receiving and transmitting circularly polarized RF signals are obtained, according to one embodiment of the invention, by providing an N-helical-filar antenna with N radiating elements coaxially arranged and defining a cylindrical envelope where each individual radiating element has a meandering shape overlaid on the main helical form and where each individual radiating element is capacitivly coupled to its neighbor in at least one end distal from the feeding point.
An advantage with the present invention is that a smaller antenna can be achieved for receiving and transmitting circularly polarized RF signals.
Another advantage with the present invention is that one antenna can be used for receiving and transmitting circularly polarized RF signals in more than one band.
Another advantage with the present invention is that only one antenna is needed both for receiving and transmitting circularly polarized RF signals even when the band for receiving RF signals is widely separated from the band for transmitting RF signals.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.